I work in maintenance at a home for abused, neglected, etc children. We have 20 bathroom sinks (4 sinks per house with 5 houses) this facility was built 6 years ago. All the sinks use an under sink vent, not vented thru the roof. Recently some of the bathrooms have developed an odor which gets stronger the closer you get to the vent. Can these vents be cleaned out somehow or should I just replace them as odors arise?
Sometimes these charity facilities have work "donated" to them, and it might not be the most experienced plumber, electrician, or whatever doing the job. You might want to get a trusted, experienced plumber to look over the install to make sure there's not something fundamentally wrong.
That said, and assuming the vents are installed correctly, the design of your particular vent will determine if it can be cleaned or not. In a lot of cases a plumber would just replace the vent because it's not worth their time to try and clean it, and hope it still works. If you're a full time maintenance person at the facility (or a DIY'er), you have time to try and clean them and then replace if they don't work since you're there all the time any way (no trip charges, driving, etc).
For instance, in this article, the guy just replaces the vent because it was so nasty, but maybe he could have soaked it for an hour and scrubbed it out. Or maybe he just knew it would never work right because he'd done it before...
Short version: Try to clean them if you think it's worth it, but you might just have to replace it anyway.